In tractor cabs that are specified for the application of sprayed materials according to ASAE S525 with a particle size of 3 μm, a particle reduction ratio of 50:1 from the surroundings to the interior of the cab is required. Despite a corresponding layout of the spray and air circulation system, the permanent maintenance of this reduction ratio is not always guaranteed. Problems may occur, for example, if the maximum allowable operating time of the filters is exceeded due to improper maintenance, if damage to the cab remains undiscovered, if aging of the cab seals occurs or if the cab sealing no longer meets the requirements due to improper repair operations. In particular, during the application of particles that are toxic or harmful to health, the maintenance of a pre-determined maximum load within the compartment, particularly in the interior of the cab, must be guaranteed.
DE-U-93 12 523 describes an arrangement for the monitoring of the operating time of filter arrangements in heating and ventilating installations, in which the compartment air is conveyed by means of a blower through a channel in which a filter is arranged. A sensor is arranged on each side of the filter for the measurement of the concentration. An input arrangement is provided with a tank for a test medium, a pump and an inlet nozzle arranged in the in-flow region ahead of the filter. A test medium is injected automatically in pre-determined time intervals through the inlet nozzle. A control arrangement monitors the signals of the two sensors and activates an optical and/or acoustic signal whenever the values of the concentrations ahead of and behind the filter approach each other, which can be ascribed to a reduction in the filter capacity. This arrangement requires two sensors and a relatively costly input arrangement for a test medium. Therefore, it is uneconomical and inappropriate for a number of applications.
The problem underlying the invention is seen in the need to define an arrangement for the monitoring of the degree of contamination of the air in a closed compartment of the type cited initially through which the aforementioned problems are overcome and the requirements are attained. In particular, the arrangement should also be appropriate for the monitoring of particles that are toxic or harmful to health. It should make possible a reliable detection of poisonous quantities and protect persons from damaging air pollution. Beyond that, it should make possible an evaluation of the filter system according to the actual load, so that a filter change is performed on the basis of the degree of contamination and not merely after the expiration of fixed maintenance intervals.